The present invention relates to an aqueous-alkaline developer solution for radiation-sensitive, positive-working reproduction layers based on silicates and at least one further component, and to a process for developing said layers.
Radiation-sensitive reproduction layers are used, for example, in the preparation of offset printing forms or of photoresists (below, both these are called copying materials), that is to say they are in general applied by the user or the manufacturer to a support. The supports used for these copying materials are metals, such as zinc, magnesium, chromium, copper, brass, steel, silicon, aluminum or combinations of these metals, plastic films, paper or similar materials. These supports can be coated with the radiation-sensitive reproduction layer without any modifying pretreatment, but preferably they are coated after carrying out a surface modification, such as mechanical, chemical and/or electrochemical roughening, an oxidation and/or treatment with agents rendering the surface hydrophilic (for example, in the case of supports for offset printing plates). In addition to at least one radiation-sensitive compound, the conventional reproduction layers contain in most cases also an organic binder (resins or the like) and, optionally, also plasticizers, pigments, dyes, wetting agents, sensitizers, adhesion-promoters, indicators and other customary auxiliaries. After they have been exposed, the reproduction layers are developed in order to produce an image from them. For example, a printing form or a photoresist is obtained in this way.
A developer for positive-working reproduction layers must be capable of dissolving those parts of the layer which have been struck by electromagnetic radiation (the later non-image areas) away from the exposed layer without substantially affecting those parts of the layer which have not been struck by the radiation (the later image areas).
In German Patent No. 12 00 133 (equivalent to U.S. Pat. No. 3,110,596), which can be mentioned as a representative example, the following are listed as examples of suitable developers: alkaline-aqueous solutions of phosphates, silicates, fluorosilicates, stannates, fluoroborates or fluorotitanates, which may additionally contain water-soluble hydrocolloids or organic solvents.
Various alternatives or modifications have been proposed by the prior art in order to improve these aqueous-alkaline developer solutions.
German Offenlegungsschrift No. 28 34 958 (=ZA-PS No. 79/4131) describes a process for developing positive-working light-sensitive layers based on o-naphthoquinone diazides and alkali-soluble resins, in which the exposed areas of the layer are washed out with a developer solution containing (a) a substance having an alkaline reaction, such as water glass, sodium metasilicate, Na.sub.3 PO.sub.4, K.sub.3 PO.sub.4, Na.sub.2 HPO.sub.4, K.sub.2 HPO.sub.4, NaOH, KOH, diethylamine, ethanolamine, or triethanolamine, and (b) a salt, oxide or hydroxide of an element of the groups IIa, IIIa or IIIb of the Periodic Table, such as calcium, strontium, or barium.
British Pat. No. 1,591,988 discloses a developing method for positive-working, light-sensitive layers which are based on o-naphthoquinone diazide esters and alkali-soluble resins, by means of a developer containing (a) 75 to 99.5 percent by volume of an aqueous-alkaline solution, for example, of Na-metasilicate or Na.sub.3 PO.sub.4, and (b) 0.5 to 25 percent by volume of an organic solvent, such as alkanols or alkane diols (or the monoethers thereof). Further components mentioned in the specification are NaOH, Na-benzoate, dimethylformamide, polyethylene glycol, Na.sub.2 HPO.sub.4 and tetrasodium ethylenediamine tetraacetate.
In IBM Technical Disclosure Bulletin, Vol. 13, No. 7, 12/1970, page 2,009 M. J. Grieco et al. state that aqueous-alkaline or alcoholic-alkaline solutions which do not contain Na.sup.+ ions, which have a pH range of from 9 to 13 and contain between 5 and 25 percent of tetramethylammonium hydroxide can be used for developing positive-working photoresists.
In the production of semi-conductor layers in accordance with Japanese unexamined patent application No. 158 280/75 (published Dec. 22, 1975), positive-working photoresists based on o-naphthoquinone diazides and novolak resins are developed with an aqueous solution containing between 1 and 4 percent by weight of tetramethylammonium hydroxide.
In Japanese examined patent application No. 4423/78 (published Feb. 17, 1978), aqueous or alcoholic solutions of tetraalkylammonium hydroxide (alkyl C.sub.1 to C.sub.7) are described as suitable developers for positive-working photoresists based on o-naphthoquinone diazides and novolak resins. Tetrahydroxyethylammonium hydroxide is also mentioned as a developer component, but said to be less suitable.
From German Offelegungsschrift No. 23 12 499 (equivalent to British Pat. No. 1,367,830), positive-working photoresists based on diazoquinone siloxanes and alkali-soluble binders are known, which are developed by means of an aqueous solution containing 1.7 percent by weight of tetramethylammonium hydroxide and an anionic surfactant.
The developer for positive-working, quinone diazide-containing, light-sensitive layers used for photoresists and printing plates, according to U.S. Pat. No. 4,141,733, contains 1 to 30 percent by weight of methyltrihydroxy-ethylammonium hydroxide in an aqueous solution. In comparative examples, tetramethylammonium hydroxide, tetraethylammonium hydroxide, benzyl-methyldihydroxy-ethylammonium hydroxide and benzylhydroxy-ethyldimethylammonium hydroxide are likewise used.
In accordance with the teaching of European Offenlegungsschrift No. 0 023 758 (equivalent to U.S. Pat. No. 4,294,211) quarternary ammonium hydroxides possessing at least one hydroxyalkyl group can be stabilized in developers by adding sulfites, hydrosulfites or pyrosulfites (disulfites, metasulfites).
However, all these known developers still have various disadvantages, for example, they often attack the aluminum oxide layer on the support materials of the printing plates, or they result in a gradation which is too flat (not sufficiently steep) in the image areas.